Vilyuisk encephalomyelitis (VE) is a progressive neurological disorder of unknown etiology with a fatal outcome that affects the Yakut people of Siberia. Dementia usually develops during the progression of the disease in most of the patients. Inheritance of ApoE-M4 allele has been shown to be a risk factor in developing of late onset Alzheimer's disease. Genetic analysis of the ApoE allele distribution performed in general Yakut population revealed that the frequency of M2, M3, M4 (0.09, 0.72, 0.19), alleles is similar to the European population. The group of chronic VE patients without dementia had the same ApoE allele frequency as controls, but the group of patients with dementias had a two-fold higher M4 allele frequency compared to the first group and controls.